What is substitution in math terms?

Answer 1

If you have a problem like this:

x=y+4 (1)

8y+2x=58 (2)

...the substitution method is the best way of working out the values of X and Y.

We know that x is the same as y + 4, so we can replace the x in equation two with y+4. This changes equation 2 to:

8y+2(y+4)=58

We now need to expand the brackets, giving us...

8y+2y+8=58

The next step is to tidy up the equation. To do this, we should firstly simplify the two y terms as they have the same coefficient, and remove the 8 from the left side, giving us...

10y=50

Obviously, we now have to divide 50 by y, to give us:

y=5

We now know y, so by rearranging formula 1 a little, we get:

x-4=y

We know that y = 5, so x-4 is 5. We add 4 to the 5 to remove the -4 from the left side, leaving us with x=9.

Let's check if this works:

9=5=4 CORRECT

40+18=58 CORRECT

It works!